(1) Field of the Invention
This invention relates to a device for sensing the local gravitational field so as to provide a roll or pitch sensor. The device of the present invention, in combination with other sensors, may be used to determine the shape of a towed hydrophone array.
(2) Description of the Prior Art
Sensors which employ optical fibers to measure physical motion of a structure are known in the prior art. For example, U.S. Pat. No. 4,788,868 to Wilk; U.S. Pat. No. 4,654,520 to Griffiths; and U.S. Pat. No. 4,812,645 to Griffiths illustrate structural monitoring systems using fiber optics. U.S. Pat. No. 4,806,012 to Meltz et al. illustrates a distributed, spatially resolving optical fiber strain gauge in which the core of the optical fiber is written with periodic grating patterns effective for transmitting and reflecting light injected into the core. Spectral shifts in the transmitted and reflected light indicate the intensity of the strain or temperature variations at positions of the grating corresponding to the associated wavelengths of injected light. U.S. Pat. No. 5,012,679 to Haefner illustrates an optical sensor which uses a beam waveguide embedded in a force or pressure transmitting material, in particular an elastomer. To be used as a force measuring sensor, the bean waveguide is mounted on an elastic deformable body and embedded in a material that does not undergo creep under the influence of a force. None of these sensors have utility as a roll or pitch sensor.
Some towed hydrophone arrays require precise determination of their shape in the water. This has been done in the past with gimbaled heading sensors. These devices are quite expensive. It is desirable to reduce cost in the towed array. Fiber optic hydrophone systems are under development and it is desirable to provide shape sensing that is compatible and that reduces the cost of the shape sensing.
An alternative way to determine array shape is by curvature sensors and either roll or twist sensors. Roll sensors have the advantage of sensing an absolute parameter at each point measured.
Accordingly, it is an object of the present invention to provide a fiber optic sensing device which may be used as a fiber optic roll sensor or as a fiber optic pitch sensor.
It is yet another object of the present invention to provide a fiber optic sensing device which may be used as a fiber optic roll sensor or as a fiber optic pitch sensor in a towed array.
It is a further object of the present invention to provide a sensing device as above which is simple and relatively inexpensive.
The foregoing objects are attained by the sensing device of the present invention.
In accordance with the present invention, a sensing device is provided which may be used as a roll sensor and/or as a pitch sensor. The sensing device broadly comprises at least one optical fiber supported in a structure, a movable mass supported within the structure, and means for detecting changes in tension in the at least one optical fiber due to movement of the movable mass. The only deformable structure in the sensing device of the present invention is the optical fiber(s), thereby maximizing sensitivity.
Other details of the sensing device of the present invention, as well as other objects and advantages attendant thereto, are set forth in the following detailed description and the accompanying drawings wherein like reference numerals depict like elements.